Percussive tools and machines



July. 22, 1969 D. R. JAMES 3,45 ,142

PERCUSSIVE TOOLS AND MACHINES Filed July 5, 1967 4 Sheets- Sheet l INVENTOR DAV/0 mammal/0446s ATTORNEYS July 22, 1969 JAMES 3,456,742

PERCUSSIVE TOOLS AND MACHINES Filed July 5, 1967 4 Sh99tS-Sh89t 2 Fla. 2.

l INVENTOR .Dnwo Elm/men c/HMES ATTORNEYS y 1969 D. R. JAMES 3,456,742

PERCUSSIVE TOOLS AND MACHINES v Filed July 5, 1967 4 Sheets-Sheet 5 INVQENTOR Dav/0 19/0/1421) JHMES ATTORNEYS July 22,1969 D. MAME; 3,456,742

PERCUSSIVE TOOLS AND MACHINES Filed July 5, 1967 4 Sheets-{Sheet 4.

" INVENTO DAV/0 flan/m0 MES BY v ATTORNEYS U.S. Cl. 173116 10 Claims ABSTRACT OF THE DISCLOSURE A percussive tool or machine derives motive power from a series of hydraulic pressure pulses. The percussive tool or machine has a pressure chamber to which in use the hydraulic pulses are supplied and a piston mounted for reciprocation in the chamber, the pressure pulses acting to move the piston in one direction and spring means acting to move the piston in the return direction. A further chamber in use is filled with liquid which provides a liquid medium through which the spring means act on the piston, and a pressure balance valve in the non-running position places the chambers in communication one with the other to relieve any excess pressure in the chamber which may have built up during the previous running period.

This invention relates to percussive tools and machines, hereinafter referred to generally as percussive mechanisms and of the type which derive motive power from a series of hydraulic pressure pulses. The invention is of particular but by no means exclusive application to a tool or machine which forms the receiver of a power transmission system of the type, sometimes referred to as an alternating flow or A.F. hydraulic system, in which an alternating pressure hydraulic pulse generator is connected through a power line, normally in the form of a single flexible hydraulic hose, to the receiver. Road breakers, rock drills and forging hammers are specific examples of tools with which the invention can with ad vantage be employed.

Tools and machines of the type concerned normally have a piston, reciprocation of which in one direction results from the pressure pulses and in the opposite direction is caused by spring means. The object of the invention is to provide such a tool or machine provided with automatic control means which assist in maintaining steady and optimum running conditions in spite of increasing working temperature and leakage from a pressure chamber to which the hydraulic pulses are supplied.

According to the invention a percussive tool or machine has a pressure chamber to which in use hydraulic pressure pulses are supplied, a piston slidably mounted for reciprocation in said chamber, the pressure pulses acting to move the piston in one direction and spring means acting to move the piston in the return direction, a further chamber which in use is filled with liquid to provide a liquid medium through which the spring means act on the piston, and a pressure balance valve which in the non-running position acts to place the pressure and further chambers in communication one with the other to relieve any excess pressure in the further chamber.

Thus whenever the tool or machine is not actually in operation the two chambers are placed in communication to relieve any adverse pressure rise in the further chamber and restore balanced conditions. The tendency for a pressure rise results from thermal expansion as the working temperature increases, due to internal friction and other causes, and also to some extent from leakage from the pressure chamber.

The balance valve may in some constructions be a simple check valve which, when the tool or machine is States Patent running, is maintained closed by the higher pressures which then obtain in the pressure chamber. The further chamber may be an intermediate chamber between the piston and the spring means, although alternatively the liquid in that chamber may be compressed during piston reciprocation to provide the spring action itself with the liquid acting as a hydraulic spring.

The further chamber may be divided into two portions separated by a transverse wall with an aperture through which the piston passes and which, during idle running, is effectively closed by an increased diameter portion of the piston as the latter approaches the end of the outward stroke. When this occurs the liquid in the portion of the chamber adjacent the pressure chamber is compressed and acts as a hydraulic spring which arrests the piston, energy being stored which is recovered on the next inward stroke of the piston. The effect is to prevent overstroking of the piston and attendant damage of the parts due to mechanical impact. With such a construction the balance valve cannot normally take the form of a simple check valve and the balance valve is preferably incorporated in control means which must be operated to bring the tool or machine into operation, and which when in the idle condition conveniently place the pressure chamber in communication with both portions of the further chamber.

Arresting of the piston to prevent over-stroking can alternatively be achieved by a dashpot action, and to obtain this the increased diameter portion may restrict rather than close the aperture between the two chamber portions. The dashpot chamber portion adjacent the pressure chamber can be of relatively small volume as compared with a hydraulic spring chamber portion, and it may be provided by a bore in a sleeve which surrounds the piston and which is entered with slight clearance by the increased diameter piston portion.

The control means may comprise a slidable valve member which is spring-loaded towards the idle position from which it must be displaced manually to a run position by the machine or tool operator. Movement of the valve member may control electrical contacts, one of which is conveniently mounted on the valve member so that the contacts close in the run position thereof, with the contacts providing remote control for a hydraulic control valve associated with a pulsatory pressure source to which the machine or tool is in use connected through a power line.

Movement of the slidable valve member may be by way of a thumb button, mounted on or formed integrally with the valve member, or by means of a hand control lever.

The invention will now be further described with reference to the accompanying drawings which illustrate, by way of example, two forms of road breaker hammers in accordance with the invention.

In the drawings:

FIGURE 1 illustrates somewhat diagrammatically an axial cross-section of one of the hammers, drawn mainly to illustrate the basic features of the invention,

FIGURE 2 is a side view of the other hammer, partly in axial section,

FIGURE 3 is an axial section on the line III--III in FIGURE 2,

FIGURE 4 is a view to a larger scale of the sectioned part of FIGURE 2, and

FIGURE 5 is a sectional view of a modified form of valve for the hammer of FIGURES 2 to 4.

In each case the hammer in use forms the receiver of an A.F. hydraulic power system, and comprises a generally tubular body 1 in the forward end of which a replaceable drill bit '2 of conventional form can be mounted. Only the upper end portion of the drill bit is shown in the drawings. An integral piston and striker 3 3 of cylindrical stepped form is slidable coaxially within the body 1 and has a forward end section 3a of reduced diameter the free end 4 of which provides a striking face which strikes the bit 2 during a forward power stroke of the piston and striker 3.

The body 1 of the hammer is formed in sections 1a, 1b and 10 which between them define three chambers, namely a pressure chamber 5 with a connection 6 for a flexible hose 7 providing the power line of the power system, an intermediate chamber 8 which in use is filled with liquid, and a spring chamber 9 which in use is filled with a relatively compressible fluid, for example air, under pressure.

The end section 3a of the piston and striker 3 slides through a seal 10 at the forward end of the pressure chamber 5, and an intermediate diameter section 3b slides through a seal 12 separating the pressure and intermediate chambers 5 and 8. The hydraulic pulses in the pressure chamber 5 act on the differential area provided by the step 13 between the sections 3a and 3b of the piston and striker 3 to produce movement in the rearward direction, i.e. in the sense opposite to the power stroke.

Referring now particularly to the contruction of FIG- URE l, the spring chamber 9 has oppositely dished walls, the lower of which is provided by a perforated plate 14 with the perforations 15 communicating with the rear end of the intermediate chamber 8. The upper dished wall is in the form of an end plate 16 which is bolted to and closes the upper end of the body portion 1c. A flexible diaphragm 17 across the spring chamber 9 is urged towards the perforated wall 14- by the air pressure and lies against that wall when the hammer is idle, providing an impermeable membrane between the chambers 8 and 9. On an inward stroke resulting from the application of a hydraulic pressure pulse to the pressure chamber 5 the piston and striker 3 moves further into the intermediate chamber 8, displacing the liquid therein which in turn displaces the diaphragm 17 to increase the compression of the air in the spring chamber 9. On relief of pressure in the pressure chamber 5 the air pressure acts through the liquid in the intermediate chamber 8 to provide a forward power stroke of the piston and striker 3.

The intermediate chamber 8 is divided into two portions 8a and 8b by a transverse wall 18 with a central sleeve-like restrictor formation at 19 which is a close fit with respect to the rear end section 30 of the piston and striker 3. When the tool is not loaded and is running light, as when withdrawing the bit 2 from a drilled bore, the piston and striker section 30 enters and effectively seals the restrictor sleeve 19 as the limit of the outward stroke, under the influence of the air spring, approaches. As a result the liquid in the forward portion 8a of the intermediate chamber 8 is compressed and acts as a hydraulic spring which arrests the piston and striker 3, the energy of the latter being stored in the liquid and returned to the piston and striker 3 during the next inward stroke.

During operation of the hammer the volume of liquid in the intermediate chamber 8 tends to increase, due to thermal expansion as the working temperature increases and as a result of leakage from the pressure chamber 5. If unchecked this would adversely affect performance, and in accordance with the invention control means are provided which in the non-running position place the chambers 5 and 8 in communication one with the other. As a tool of this nature works in bursts of comparatively short duration, rarely exceeding say ten minutes, the liquid volume change in the intermediate chamber 8 is negligible during a working period. The automatic correction whenever the tool is not working, and the piston and striker 3 urged to its forward limit by the pressure in the chamber 8, ensures that a satisfactory level of performance is maintained at all times. The pressure is provided by a make-up pump as later described.

The control means take the form of a slidable piston valve member 20 the upper end of which forms a thumb button 22, and which slides longitudinally of the body 1 in a valve bore 23 formed to one side in the body. At the lower end the valve member 20 has a shoulder 24 which limits upward travel, and a helical compression spring 25 fitted in a pocket beneath the valve member 20 urges the latter to its upper limit defining the nonrunning position which is illustrated in FIGURE 1. In this position the valve member 20 interconnects and provides free communication between three ports 26 to 28 which respectively communicate with the pressure chamber 5 and the two portions 8a and 8b of the intermediate chamber 8. The valve member 20 is sealed with resilient 0 rings 29 at each end of the valve bore 23, and further 0 rings 30 provide a fluid seal isolating the three ports 26 to 28 when the valve member 20 is depressed by the operator to bring the tool into operation.

An insulated electrical contact 32 is mounted in the spring pocket and a cooperating contact 33 is mounted at the lower end of the valve member 20. When the latter is depressed the contacts 32 and 33 close after the three valve ports 26 to 28 have been isolated, and in use the contacts control an outlet hydraulic valve of the hydraulic pulse generator (not shown) which supplies the pressure chamber. An electrical lead is normally run back to the generator from the contact 32 alongside the hose, the control circuit employing an earth return utilising metal reinforcing braid of the hose 7. The arrangement ensures that the pressure and intermediate chambers are isolated before power is applied to the hammer, and that the power is switched off before pressure balancing takes place by way of the valve ports 26 to 28; as mentioned previously such balancing takes place with the striker and piston moved to the forward limit of travel by the make-up pressure in the chamber 8.

Turning now to the more practical embodiment of FIG- URES 2 to 4, which were appropriate utilise the same refernece numerals as the diagrammatic showing of FIG- URE 1, the tubular body 1 is now provided with two diametrically opposed and projecting tubular handles 40 by which the hammer is held when in use. At the forward end the body has a sleeve insert 41 in which the drill bit 2 is mounted. The bit 2 is detachably retained by a retainer spring 42 mounted on the body 1.

The adjoining ends of the body portions are counterbored to house and locate seal carriers 43 and 44 of assemblies providing the seals 10 and 12, and each of which carries a duplex arrangement of lip-type seals 45 and 46 respectively. A scraper ring 47 mounted on the forward end of the carrier 43 engages the piston and striker portion 3a and provides a seal against contamination of the forward seal 10 by dirt entering the forward end of the body 1. The piston and striker 3 is hollow, having a blind bore 31 drilled from the rear end in order to reduce the inertia to suit the resonant conditions which are required to match the reciprocatory system to the frequency of the power generator, a typical operating frequency being 30 cycles per second.

The hammer is functionally similar to the construction of FIGURE 1, with a substantially incompressible liquid fluid in the chamber 8 acting as a fluid shield and transmitting the spring force from the spring chamber 9. The perforated plate 14 of the spring chamber 9 is now flat, being spaced from and parallel to the flexible diaphragm 17 when the latter is in the resting or uncharged position illustrated. The spring chamber 9 is pre-charged to the required spring pressure through a check valve 49 which is mounted centrally in the end cap 16 and protected by a screwed cover 50 which is removed to allow access to the valve. A typical operating spring pressure is lbs. per square inch, and the plate 14 has concentric rings of multiple drillings 15 which as before permit liquid transfer across the plate to and from the chamber 8 and so that the pressure in the latter always acts on the diaphram 17.

The absolute outward limit of movement of the piston and striker 3, i.e. movement in the forward power or working stroke direction, is limited by engagement of the striker face 4 with the rear end of the insert 41 as shown in FIGURE 3. This is the normal resting condition which obtains between the normally intermittent periods of use. In order to ensure that in the free-running condition the piston and striker 3 does not strike the insert 41 to produce arduous shock load conditions, with attendant noise and risk of mechanical damage, the piston and striker portion 30 enters and restricts a choke bore formed by a rear end counterbore 52 in a bush 53 which is fitted in the body portion 10, and provides an annular sleeve which surrounds the piston and striker 3 rearwardly of the seal carrier 44. Thus the counterbore 52 provides the intermediate chamber portion 8a, and as the outer limit of the forward stroke of the piston and striker 3 is ap proached some of the hydraulic liquid in the chamber 8 is trapped within the counterbore 52. Continued forward movement of the piston and striker 3 produces a high pressure in this liquid to provide a dashpot action. In operation of the hammer this prevents the forward position of the piston and striker 3 illustrated in FIGURE 3 being reached, and this is so even when the hammer is free running. The liquid compressed in the counterbore 52 is ejected from the latter through the restriction provided by the small annular clearance between the piston and striker portion 30 and the counterbore 52, and in the illustrated construction this clearance is of the order of two thousandths of an inch.

Operation of the hammer is controlled by means of an operating lever 54 which is pivotally mounted on the body portion 10 at 55. The lever 54 overlies one handle 40 and is connected through a link 56 to the valve member 20. The valve member 20 operates generally in the manner already described and, as shown in greater detail in the larger scale view of FIGURE 4, is slidable in a ported sleeve 57 mounted in a bore 58 formed partly in the body portion 1b and partly in the adjacent body portion 10 alongside the seal carrier 43. The sleeve 57 is sealed relatively to the valve bore 58 by rings 59, and the lowermost ring 59 has an anti-extrusion ring 60 mounted alongside it in the valve member 20. The springloaded moving electrical contact 33 is again mounted on the lower end of the valve member 20 for cooperation with the fixed insulated electrical contact 32 which is now mounted above it.

To operate the hammer the lever 54 is gripped to the adjacent handle 40, instead of depressing the button 22 of FIGURE 1, and this closes the contacts 32 and 33 and moves the valve member 20 against the valve spring 25 to the run position illustrated in FIGURES 2 and 4.

In the run condition of the valve member 20- shown in FIGURES 2 and 4, ports 62 and 63 in the valve sleeve 57, which respectively communicate with the pressure chamber and the intermediate chamber 8, are as shown blanked off by the valve member 20 so that they do not communicate and hence the chambers 5 and 8 are isolated one from the other during the operation of the hammer. As the chamber portion 8a provided by the counterbore is now so small in relation to the portion 8b the valve only requires two ports 62 and 63, instead of the three ports 26 to 28 of the arrangement of FIGURE 1 in which the chamber portions 8a and 8b are of comparable volume. The ports 62 and 63 are provided by radial drillings through the sleeve 57, which drillings respectively communicate with external annular grooves 64 and 65 in the sleeve. These grooves are sealed by respective pairs of the 0 rings 59, and they communicate with the chambers 5 and 8 through drillings 66 and 67 in the walls of the body portions 11) and 10.

On release of the lever 54 the valve member 20 is returned by the spring 25; as a result the contacts 32 and 33 open to de-energise (as before) the control valve at the generator and hence reciprocation of the piston and striker 3 ceases. The valve member 48 moves to a resting position in which an axial bore 68 in that member, which bore is closed at both ends, interconnects the ports 62 and 63 via radial drillings 69 between that bore and peripheral annular grooves 70 in the valve member 20. The valve member 20 slides in a stepped bore 72 of the sleeve 57, and the operative section of the valve member containing the drillings 69 and the grooves 70 is contained within the smaller diameter section of the bore 72, which contains the ports 62 and 63. The larger diameter section of the bore 72 houses the valve spring 25, and is closed by an annular plug 73 which is retained by a circlip 74 and sealed externally by an O ring 75. The valve member 20 slides through the plug 73 and is sealed relatively thereto by an O ring 76 with anti-extrusion ring 77; it is sealed relatively to the bore 72 by 0 rings 78, the lower of which has an anti-extrusion ring 79.

The hydraulic system includes a make-up pump (not shown) which tends to maintain a minimum hydraulic pressure of say 80 lbs. per square inch, and maintains this pressure when the generator is inoperative as a result of the contacts 32 and 33 being open. This condition as described corresponds to a valve position in which the chambers 5 and 8 intercommunicate, and ensures that when the hammer is idle the chamber 8 is pre-charged to the make-up pressure ready for operation. The make-up pressure is also applied to the rear end of the piston and striker 3, with resultant movement of the piston and striker to the forward limit position illustrated in the drawings against the opposition of the same hydraulic pressure acting on the relatively small step between the portions 3a and 3b in the pressure chamber 5. Thus movement of the valve member 20 to the idle position not only ensures that the chamber 8 is precharged to the correct pressure but also that it contains the correct volume of hydraulic liquid, i.e. the volume corresponding to the forward limit defined by abutment of the piston and striker 3 with the insert 41.

Thus the automatic spring-loaded operation of the valve member 20 assist in maintaining steady and optimum running conditions, immediately after use the liquid in the chamber 8 being correctly adjusted as regards both pressure and volume. During setting up of the hammer with the make-up pump running the valve member 20 provides for pre-charging of the chamber 8, any air being displaced past a bleed screw 80 which is slackened off for the purpose. with the correct pressure condition in the chamber 8 the spring chamber 9 can be pre-charged with compressed air to the correct spring pressure, and the hammer is then ready for use by operation of the lever 54.

The use of the fluid shield provided by the hydraulic liquid in the chamber 8, together with the flexible diaphragm 71, in both constructions provides a particularly convenient manor of utilising a pneumatic spring as there are no problems or air leakage from the spring chamber 9 or of contamination by leakage from the pressure chamber 5, and yet th spring force is applied satisfactory and directly to the piston and striker 3. The liquid in the chamber 8 in effect acts a liquid connecting rod, and what can be termed a hydro-pneumatic spring system results. As an example of typical operating conditions, with the spring chamber 9 pro-charged to a pressure of lbs. per square inch a maximum spring pressure of 380 lbs. per square inch results with a hydraulic operating pressure the pulses of which produce pressure variations between 60 and 1800 lbs. per square inch at an operating frequency of 30 cycles per second.

The modified form of valve illustrated in FIGURE 5 is entirely automatic in operation and does not embody the electrical contacts 32 and 33 which are provided in a separate control switch. The switch, which is not illustrated is mounted on one of the handles 40 and merely serves to control the hydraulic pulse generator and is closed when it is desired to operate the hammer. The valve again comprises a valve member 20 which is slidable in a ported sleeve 57 mounted in a bore 58 formed partly in the body portion 1b and partly in the adjacent body portion 1c. The upper end of the bore 58 is now closed above the sleeve 57, and the bottom end is sealed by a cylindrical plug 82 having a cylindrical central projection 83 with a diametral cross slot 84. The projection 83 provides an abutment defining the resting position of the valve member 20 shown in FIGURE and to which it is urged by the valve spring 25, and the region of the bore 58 surrounding the projection 83 communicates with the pressure chamber 5 through the drilling 66 in the body portion 112. The sleeve 57 now has only the one set of radial drillings 63 communicating with the external annular groove 65 which, as before, communicates with the chamber 8 through the drilling 67 in the wall of the body portion 1c.

The valve member 20 has a stem portion which slides in the sleeve 57 and in the resting position illustrated is positioned just below the porting 63, and a lower end flange 85 which is sealed with respect to the bore 58 by an O ring 86 slides in that bore between the lower end of the sleeve 57, which defines the upper limit of valve movement, and the plug 82. An 0 ring 87 seals the plug 82 within the bore 58, and further 0 rings 88 seal the sleeve 57 on opposite sides of the annular groove 65. In the resting valve position illustrated in FIGURE 5, i.e. with the hammer not operating, the chambers 5 and 8 as before are placed in communication through the slot 84 in the plug 82 and a central bore 89 in the valve member 20. This balances the pressure in these two chambers and in the manner described pre-charges the chamber 8 to the make-up pressure of the system.

When the control switch is closed the valve member 20 is subjected to unbalanced pressure conditions, the pressure in the pressure chamber 5 acting on the one hand on the annular end area of the flange 85 and on the other hand on the very much smaller upper end annular area of the valve member 20. The pressure also acts upwardly on a small step 90 within the bore 89 in the valve member 20, and the resultant differential force on the valve member 20 is suflicient to overcome the force of the valve spring 25 and moves the valve member 20 to its upper limit. This blanks oif the porting 63 so that the chambers 5 and 8 no longer communicate, and the valve member 20 remains in this position until operation of the hammer ceases as a result of the control switch being opened.

Instead of utilising the electrical contacts of the control means, 32 and 33 in FIGURES 1, 2 and 4, for remote operation of a control valve at the generator they may be utilised to control hammer operation in other ways. For example they may operate to control a clutch in a mechanical drive of the hydraulic pulse generator, or they may control an electrical relay which in turn controls an electric driving motor of the generator.

I claim:

1. A percussive mechanism comprising a pressure chamber, means for supplying hydraulic pressure pulses to said chamber, a piston slidably mounted for reciprocation in said chamber with the pressure pulses acting to move the piston in one direction, spring means acting to move the piston in the return direction, a further chamber which in use is filled with liquid to provide a liquid medium through which the spring means act on the piston,

and a pressure balance valve which in the nonrunning position acts to place the pressure and further chambers in communication one with the other.

2. A percussive mechanism as claimed in claim 1, said balance valve having a valve member which is spring loaded to the open position and which is manually movable to the closed position in which it is to be held during operation of the mechanism.

3. A percussive mechanism as claimed in claim 2, and electrical contacts controlled by movement of the valve member to provide remote control for said supply means 4. A percussive mechanism as claimed in claim 1, said balance valve operating automatically and having a valve member which is spring loaded to an open nonrunning position, and means responsive to the pressure which obtains in the pressure chamber during running position to close said valve member.

5. A percussive mechanism as claimed in claim 1, said further chamber being an intermediate chamber disposed between the piston and the spring means.

6. A percussive mechanism as claimed in claim 1, and means dividing said further chamber into two portions with an aperture communicating therebetween through which the piston passes, said piston having an increased diameter portion which restricts said aperture as the piston approaches the end of the outward stroke.

7. A percussive mechanism'as claimed in claim 6, said dividing means comprising a transverse wall, said piston effectively closing the aperture and compressing the liquid 'in the chamber portion adjacent the pressure chamber whereby the compressed liquid acts as a hydraulic spring which arrests the piston.

8. A percussive mechanism as claimed in claim 7, said balance valve having three ports which are interconnected in the nonrunning valve condition, said ports communicating respectively with the pressure chamber and the two portions of said further chamber.

9. A percussive mechanism as claimed in claim 6, said increased diameter piston portion restricting said aperture so that the arrest of the piston is achieved by a dashpot action in one of said chamber portions, said dashpot chamber portion being of relatively small volume as compared with the remaining portion of said further chamber.

10. A percussive mechanism as claimed in claim 9, said balance valve having effectively only two ports which are interconnected in the nonrunning valve condition, one of said two ports communicating with said further chamber and the other of said two ports communicating with the remaining portion of said further chamber.

References Cited UNITED STATES PATENTS US. Cl. X.R. 173-119, 137 

